Visible wavelength, semiconductor optoelectronic device with a high power broad, significantly laterally uniform, diffraction limited output beam

ABSTRACT

A Group III-V semiconductor optoelectronic device provides for visible wavelength light output having a more laterally uniform, high power beam profile, albeit still quasi-Gaussian. A number of factors contribute to the enhanced profile including an improvement in reducing band offset of the Group III-V deposited layers improving carrier density through a decrease in the voltage drop required to generate carrier flow; reduction of contaminants in the growth of Group III-V AlGaInP-containing layers with compositional Al, providing for quality material necessary to achieve operation at the desired visible wavelengths; the formation of an optical resonator cavity that provides, in part, weak waveguiding of the propagating light; and the utilization of a mechanism to provide for beam spreading and filing in a beam diverging gain section prior to actively aggressive gain pumping of the propagating light in the device.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 08/650,704 filedMay 20, 1996, now U.S. Pat. No. 6,181,721, which is incorporated hereinby its reference.

FIELD OF THE INVENTION

This invention relates generally to visible wavelength, semiconductoroptoelectronic devices for producing high power diverging beam outputand, more particularly, to visible laser devices generating light withinthe 600 nm to 700 nm wavelength range that provide a broad, high poweroutput beam.

BACKGROUND OF THE INVENTION

Since about 1987, in particular, there has been much published aboutsemiconductor lasers that are capable of emitting light within the 600nm to 700 nm wavelength range for use in many applications, such asoptical disc apparatus, laser printers, bar code readers and the like.An example of an earlier article on this subject is the paper of K.Kobayashi et al. entitled, “AlGaInP Double heterostructure Visible LightLaser Diodes with a GaInP Active Layer Grown By Metalorganic Vapor PhaseEpitaxy”, IEEE Journal of Quantum Electronics, Vol. QE-23(6), pp.704-711, June 1987. These devices include ternary and quaternary GroupIII-V materials including In, P or InP for achieving visible lightwavegeneration. The devices have an active region of GaInP or AlGaInPlattice matched or coherently strained to a GaAs substrate with claddinglayers of AlGaInP and confinement layers of AlInP. The active region maybe a single quantum well of GaInP or multiple quantum well structure ofGaInP well layers and AlGaInP barrier layers or alternating layers ofAlGaInP of different compositional ratio. A more recent publication isU.S. Pat. No. 5,144,633 to Ohnaka et al. which is discloses a visiblewavelength, semiconductor laser device having an active region of GaInPlattice matched to a GaAs substrate, with cladding layers of AlGaInP andat least one confinement layer of AlInP. A stopper layer of GaInP (dopedor undoped) is usually formed within the AlInP confinement layer foraiding in an etching operation to form a buried or inner loss-guidestripe region through a subsequently formed current blocking layer ofGaAs.

A problem in these devices is the confinement of carriers to the activeregion and provision for a low resistance path for carrier supply to theactive region. This problem is addressed, in part, in U.S. Pat. No.5,274,656 to Yoshida. In this patent, reference is made to the fact thathigher Al composition ratios in the cladding layers are preferable forefficient confinement of carriers to the active region. However, ithappens that such higher Al composition ratios bring about more heatgeneration affecting the long term reliability of these devices.Attempts to decrease the resistivity of the cladding layers throughdecrease of the layer resistivity through increase the doping level ofthe layer is not effectual for AlGaInP layers, for example, because thedoping activation ratio level is reduced as Al content increases. Inorder to achieve shorter wavelengths into the visible spectrum, thebandgap of the active layer can be increased, but the difference inbandgap between the active region and the cladding region becomescloser, decreasing the carrier confinement to the active region. Yoshidaprovides an upper cladding layer comprising AlGaInP that decreases in Alcomposition ratio from its inner most limit closest to the GaInP activeregion to its outer most limit. The overall Al composition ratio islowered so that carrier density in at least the outer reaches of thecladding layer is increased without need of increasing the layer dopinglevel. However, further reductions in forward voltage drop are desiredin cladding layer areas of these devices, particularly in the case wherenarrow pumping stripes are employed with broad area beam output withhigher output power.

Thus, the problem still persists on how to further reduce the voltagedrop in these cladding layers to provide a low resistance path to theactive region without sacrificing high carrier confinement to the activeregion. This is particularly important in visible wavelength,semiconductor devices that are designed to provide a high level ofpower, such as employing on the same semiconductor chip or on adifferent semiconductor chip, a single mode section and a gain sectionfor achieving high power. One such device comprises a master oscillatorin combination with a beam enlarging or diverging gain section providinga beam diverging phase front forming a stable oscillator. Another suchdevice comprises a single mode section and a diverging gain sectionutilizing a beam diverging phase front forming an unstable oscillator.Such devices are disclosed in the U.S. Pat. Nos. 5,539,571 and5,537,432, which patents are assigned to the assignee herein and areincorporated herein by their reference. These devices demand highercarrier concentration and carrier supply to a comparatively narrowstripe region (e.g., in the range of about 3 μm to about 5 μm wide)compared to the broad diverging gain pumping region and requiring goodcarrier conversion efficiency in the single mode section throughenhanced carrier supply. One manner of accomplishing good carrierconversion efficiency is to provide a wider pumping stripe for thesingle mode section, but a wider pumping stripe means a larger apertureinto the diverging gain region which can result in poor beam formationand divergence.

What is needed for these combination single mode and beam enlarging gainresonator devices is to enhance the carrier density through a decreasein the layer voltage drop to improve the conversion efficiency ofcarriers in the single mode section while providing good beam divergenceinto the beam diverging gain section providing an improved flatteningand broadening of the Gaussian beam profile.

It is, therefore, a primary object of this invention to provide avisible wavelength, semiconductor optoelectronic device with high CWpower, diffraction limited, visible beam.

It is another object of this invention to provide good beam divergencewith improved flattening and broadening of the Gaussian beam profilewith enhancement to beam edges by permitting the beam to initiallyexpand before more full and aggressive pumping is applied in widerregions of the beam diverging gain section with accompanying highcarrier conversion efficiency in a stable or unstable resonator lightemitting devices having a single mode section and a beam diverging gainsection.

It is a further object of this invention to improve the quality ofgrowth of sensitive Group III-V, AlGaInP-containing materials employedin the active region and confining and cladding layers of visiblewavelength, semiconductor optoelectronic devices.

It is a still further object of this invention to improve the formationand utility of high resistance regions in forming beam diverging gainsections employed in high power, visible wavelength, semiconductoroptoelectronic devices.

SUMMARY OF THE INVENTION

According to this invention, a visible wavelength, semiconductoroptoelectronic device with high CW power and diffraction limited,visible beam includes the use of Group III-V, AlGaInP-containingmaterials to achieve generation of visible wavelengths of light, such aswithin the range of 600 nm to 700 nm by reducing the band offset betweenthese materials and GaAs to improve the carrier density by means of areduction in layer voltage required to generate carrier flow whileimproving the quality of growth of AlGaInP-containing materials,particularly where these materials include compositional Al. In thepreferred embodiment, an AlGaAs layer or a combination AlGaAs andAlGaInP layer is grown between GaAs and AlGaInP-containing confinementand cladding layers, which may be index graded, at least in part, toprovide an overall reduction in the band offset between GaAs and thesematerials reducing impediment of carrier flow while permittingmaintenance of good carrier confinement in the active region. Hightemperature growth of the AlGaAs layer on a GaAs substrate also providesa gettering function in the MOCVD reactor by removal of contaminants inthe reactor that degrade the quality of the growth of AlGaInP-containingmaterials, particularly those that contain compositional Al used toachieve desired visible wavelength outputs.

Another aspect of this invention is the provision for an improvedunstable resonator optoelectronic device having a single spatial modesection functioning as a single mode spatial filter and a diverging gainsection for enhancing the power output of the beam from the device. Thesingle spatial mode section includes a three-tier current blockingregion to form the single mode spatial filter and a high current densitypumping region with loss-guiding of the propagating light in the device,and a diverging gain section that includes a light diverging regiondefined by adjacent high resistance regions formed into the Group III-Vsemiconductor structure providing for both a high gain light divergingregion as well as a small refractive index change for minimal guiding ofthe propagating light in the device. Also, the region of the diverginggain section adjacent to the single mode section, that initiallyreceives the propagating light from the single mode section, ispatterned to only provide limited pumping to this region to permit thepropagating light to initially spread and fill the diverging limits ofthe diverging gain section prior to aggressive gain pumping of thelight. This improves the saturation of the beam edges of evanescent beamtails to provide a more uniform lateral beam profile, even though thebeam retains some quasi-Gaussian appearance. The resulting unstableresonator formed between end facet reflectors of the deviceincorporating these attributes provides for both reduce voltage drop andlightwave guiding so that a more uniform beam profile with higher powercan be obtained.

The single mode section and the diverging gain section of theoptoelectronic device may be on the same chip or may be on separatechips that are optically coupled to achieve the advantages of thisinvention.

Other objects and attainments together with a fuller understanding ofthe invention will become apparent and appreciated by referring to thefollowing description and claims taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the visible wavelength, semiconductoroptoelectronic device with high beam power according to this invention.

FIG. 1A is plan view of another embodiment of the visible wavelength,semiconductor optoelectronic device shown in FIG. 1.

FIG. 2 is a cross-sectional view of the device of FIG. 1 taken along theline 2—2 of FIG. 1.

FIG. 3 is a cross-sectional view of the device of FIG. 1 taken along theline 3—3 of FIG. 1.

FIG. 4 is a bandgap diagram for the multiple layers of the device shownin FIG. 1.

FIG. 5 is a plan view of the pumping stripe pattern which is drawnfairly to scale for purposes of explaining the invention.

FIG. 6 is plan view of the device shown in FIG. 1 illustrating thepumping stripe and loss-guide configuration for the device.

FIG. 7 is a plan view of the device shown in FIG. 1 illustrating amodification to the configuration shown in FIG. 6.

FIG. 8 is a detailed plan view of a portion of the pumping stripeconfiguration shown in FIG. 5.

FIG. 9 is a detailed plan view similar to FIG. 8 but illustrating amodification to the configuration shown therein.

FIGS. 10A-10E schematically illustrate different embodiment for thediverging gain section patterned pumped region for the semiconductoroptoelectronic device of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Reference is now made to FIGS. 1 to 3 for detail explanation of thevisible wavelength, semiconductor optoelectronic device 10 with highbeam power output according to this invention. Device 10 comprises totwo principal sections, a single mode section 10A having pumping stripe26 and a beam enlarging or diverging gain section 10B having a patternof pumping stripes 27 of monotonic increasing lateral length andtrapezoidal shaped pumping stripe 28. Section 10A may include opticalfeedback means, such as DFB or DBR means in the active region, as isknown in the art, so that it will operate as an oscillator and, inconjunction with beam diverging gain section 10B, will function as astable resonator. However, the feedback means for device 10 may be endfacets 10C and 10D or internal reflectors integrated into the deviceadjacent the ends of its optical cavity of device 10 reflecting aportion of the light back into the optical cavity, providing a lightemitting device functioning as an unstable resonator. Also, as is clearfrom the previously incorporated patents, single mode section 10A neednot be on the same chip as beam diverging gain section 10B, asillustrated in FIG. 1A. Rather, section 10A can be a separate chip withits output aligned within an optical cavity that includes a chip havingdiverging gain section 10B. The two separate chips can operate within aformed optical cavity as either a stable or unstable resonator. Singlemode section 10A can be mode-locked operated in either type of these twoconfigurations and function as a stable or unstable resonator. Moreover,tuning of the wavelength of device 10 can be accomplished by means ofwavelength tuning means as taught in the U.S. Pat. No. 5,392,308,incorporated herein.

As best shown in FIGS. 2 and 3, device 10 comprises a Group III-V,AlGaInP structure preferably grown by employing conventional MOCVD.First, a n-GaAs buffer layer is typically grown. Then, a n-AlGaAstransitional layer 12 is grown on a n-GaAs substrate 11. Layer 12 may becomposed of two portions, portion 12A having an index graded content,where the Al compositional ratio is monotonically changed, and anothermuch thicker layer portion 12B of the same Al compositional ratio. Next,a n-AlInP lower cladding layer 13 is deposited on layer 12, followed bya n-AlGaInP lower confinement layer with a lower bandgap than layer 13,for purposes of carrier confinement as is well known in the art. Next,an undoped active region 15 is formed comprising a quantum well layer ofGaInP having the lowest bandgap of the light generation and waveguidestructure. Alternatively, active region 15 may comprise an InGa.AsPquantum well region with adjacent InGaAsP confinement layers of highercompositional refractive index. Active region 15 may also be a multiplequantum well region, for example, comprising well layers of GaInP andbarrier layers AlGaInP or alternating layers of AlGaInP of different Alcompositional ratio, as is known in the art. Use of two or more quantumwells in such a structure provides for lower T₀, as is known in the art.Also, active region 15 is lattice matched to the GaAs substrate 11 butmay be compressively or tensile strained to provide for slight latticemismatch to improve device performance characteristics, as is known inthe art.

Next, a p-AlGaInP upper confinement layer 16 is grown followed byp-AlInP upper/inner cladding layer 17, a p-GaInP stop etch layer 18,p-AlInP upper/outer cladding layer 19. Next, a group of transitionallayers 20, 21 are formed which are index graded by means ofmonotonically changing the Al/Ga compositional ratio in the growth ofthese layers. Layer 20 comprises p-AlGaInP and layer 21 comprisesAlGaAs. Lastly, a P⁺-GaAs cap layer 22 is formed to complete the deviceprior to pumping stripe formation and metalization.

While only one transitional layer 12 is shown in FIG. 4, it should beunderstood that two transitional layers respectively comprising n-AlGaAsand n-AlGaInP, such as similar to combination layers 21 and 20, could beutilized between n-AlGaAs layer portion 12B and lower cladding layer 13.The purpose of AlGaAs layer portion 12B is to function as a getteringagent for contaminates, such as O₂ and C, in the MOCVD reactor chamber.Group III-V, AlGaInP compounds are highly sensitive to these and othercontaminants. The compound, AlGaAs, is a getter of these contaminants.The extended period of growth of AlGaAs layer 12 represented by portion12B provides a means for cleaning up the MOCVD reactor of thesecontaminants prior to deposition of the AlGaInP-containing compounds,particularly those containing compositional Al, so that, upon the growthof the AlGaInP-containing cladding, confinement and active layers, goodgrowth properties are achieved.

Transitional layers 12, 20 and 21 provide a means for decreasing theforward voltage drop in these layers while permitting the maintenance ofgood carrier confinement to active region 15 via cladding layers 13 and17. The bandgap difference between GaAs substrate 11 and AlInP claddinglayer 13 provides for a substantial band offset representing asignificant barrier to carriers. As a result, a higher barrier is formedand the supply of carriers to active region 15 is impeded. This is ofparticular significance in the case of device 10 here where the ratio ofareas in pumping region 28 to pumping stripe 26 is large. For a givenforward voltage, only so much current density will be establishedthrough stripe 26, which may be only about 3 μm to about 5 μm wide.Since only a portion of the light is reflected back into single modesection as represented by stripe 26, it is important to achieve highcarrier density in this section so that a larger optical gain can besustained in active region 15 providing for a higher power outputdevice.

Layers 12, 20 and 21 have compositional intermediate bandgaps betweenGaAs and AlInP which have wide bandgap offset between them. With astepped increase in bandgap from GaAs to AlGaAs to AlGaInP to AlInP,these two widely different bandgap materials can be “bandgap matched”through index graded layers of AlGaAs or AlGaAs and AlGaInP by Alcompositional ratio changes to provide a monotonically distributedbandgap profile between them as illustrated in FIG. 4. As a result, thesignificant band offset between GaAs and AlInP is eliminated.

In summary, graded layers 12, 20 and 21 reduce the impediment forcarriers to transfer into active region 15 and, in the case of layer 12,the growth of a thick AlGaAs layer at high temperatures, i.e., abovearound 800° C., cleans the reactor system in which the growth is beingcarried out of contaminants so that upon initiation of the growth ofAlGaInP-containing materials, high quality growth can be accomplishedwith a reduction in band offset between the AlGaInP-containing materialsand GaAs by employing an index graded layer 12A for providing a regionstepped refractive indices and, therefore, reducing the resistance tothe passage of carriers through these layers. This combination providesfor better conversion efficiency over GaInP/AlGaInP/GaAs structures ofthe prior art.

As shown in FIG. 2, single mode section 10A, is etched back through caplayer 22, transitional layers 20, 21 and upper/outer cladding layer 19to stop layer 18 using etchants that are highly effective for removal ofAlInP but not for removal of GaInP, as is known in the art. Prior toperforming the etching operation, a portion of cap layer 22 is masked todefine stripe region 26. After performing the etching operation, aregrowth is performed comprising multiple layers 22A of GaAs forming an-p-n region to function as a current blocking region as well asfunction as a loss-guide for lightwave propagation of light in activeregion 15 propagating beneath formed stripe 26. Layers 40, 41 and 42 mayeach be, for example, about 0.3 μm thick and n-GaAs layers 40 and 42 maybe doped with Si or Se, between which is p-GaAs layer 41 doped with Znor C. The p-dopant preferred is C because of its comparatively betterstability from readily diffusing or moving into adjacent layers.

It should be realized that single mode section 10A may be operated as aself-pulsing diode laser, stable resonator device 10 which self-pulsatesunder a dc bias emitting a high frequency stream of optical pulses byincluding a saturable absorbing structure which can be quickly emptiedby diffusion of carriers to facilitate the self-pulsation function. Tosignificantly reduce the feedback sensitivity of the device, it isusefull to modulate the laser at high speeds, such as several hundredMHz. This high frequency modulation of the device destroys the coherenceof the output and renders the laser device insensitive to feedback and,therefore, low noise under a wide range of operating conditions.Unfortunately, incorporating a circuit to bias and modulate the laserdevice at high frequency considerably complicates the final system andadds additional expense. If the laser device is inherentlyself-pulsating when driven by a dc bias, an optimum operation can beachieved, however. This is accomplished by positioning a high refractiveindex, light absorbing layer outside active region 15 but sufficientlyclose to active region 15 so that it overlaps the light propagatingmode. Such a layer is comprised of a quantum well with an emissionwavelength longer than the lasing wavelength of device 10. Thisabsorbing layer may, for example, be position between the confinementand cladding layers 16, 17, comprising p-GaInP having a comparablerefractive index as active region 15. Alternatively p-GaInP layer 18 maybe sufficient close to active region 15 to function, as shown in FIG. 2,as a light absorbing layer having a comparable refractive index asactive region 15. Also, such a light absorbing layer can be on then-side of device 10 between layers 13, 14 or both comparably positionedabsorbing layers can be positioned on both sides of active region 15. Inany case, operation as a light absorbing layer 18 is as follows.

When device 10 is energized, the light absorbing layer has a highabsorption coefficient and begins to absorb light generated in activeregion 15. However, as carriers collect in the absorbing layer, theabsorption coefficient drops resulting in reduced loss in the lasercavity allowing the onset of a strong lasing mode in the device. As aresult, carriers are depleted in the active region below the thresholdlevel of device 10 due to the intense lasing mode and laser device 10terminates lasing mode operation. Once terminated, carriers diffusealong the absorbing layer and fall into regions of low bandgap energy,such as GaAs region 22A. Although the carriers generated in the lightabsorbing layer are confined above and below by higher bandgap claddinglayer 17, the carriers are free to laterally diffuse to the side of theridge region 26, shown in FIG. 2. Once the carriers so diffuse, theyfall from the absorbing layer into lower bandgap regrown region 22A.

Optoelectronic device 10 may be operated as a stable resonator by theinclusion in single mode section 10A optical feedback gratings forming amaster oscillator such as described in the previously incorporatedpatents. Such feedback gratings may be of distributed feedback (DFB) orof distributed Bragg reflector (DBR) configuration. As known in the art,these feedback gratings are difficult to fabricate in a device of thetype shown in FIG. 1 having an integrated diverging gain section 10B.Therefore, device 10 is a good candidate for operating as an unstable ora marginally stable resonator (i.e., an unguided waveguide) so that amore uniform lateral beam profile is obtained as is shown at 37E in FIG.5, although the beam still possesses some quasi-Gaussian contour. Facets10C and 10D are at least partially reflective, as known in the art, forforming a resonator cavity and a portion of the propagating light isinternally reflected in the device cavity. Facet 10C may be a highreflecting surface and facet 10D may be partially reflective, such asreflecting about 5% of the light output. Diverging light reflected fromfacet 10D is absorbed in regions 30 of section 10B with a very smallamount returned, straight-line, along the device optical cavity intosingle spatial filter 10A as explained and set forth in incorporatedU.S. Pat. No. 5,537,432.

In diverging gain section 10B, a pattern of current pumping regions 27and 28, defined by diverging edges 27A, is formed by rendering all ofregions 30 of section 10B of high resistance. These higher resistanceregions 30 are accomplished by means of a boron or carbon implant to adepth within upper/outer cladding layer 19, such as at about 3×10¹⁵cm⁻². The resistivity of the layered material in implanted regions 30 isrendered significantly higher forming current confinement and pumpingregions 27 and 28. While GaAs regrowth could be a consideration in theregions, the implant is preferred because the composition of theunderlying material is not changed and only a slight refractive indexdifference between pump regions 27, 28 and implanted regions 30 toprovide for current confinement to these regions with sufficientlightwave guidance, particularly important for operation as an unstableresonator, without excessive absorption and deterioration of thepropagating beam evanescent tail portions. Gain waveguiding in section10B is defined by carrier density within pumping of region 28, whichcarrier density increases as the diverging region 28 increases so thatthe effective waveguiding refractive index difference, Δn, betweenregions 28 and 30 also increases as the current density increases. Theimplant is patterned in the initial portion (identified as region 34 inFIG. 5) of section 10B via selective masking to form the plurality ofpumping stripes 27 to only partially pump the light beam as it exitsfrom single mode section aperture 23.

It should be realized that the pattern of stripes 27 in FIG. 1 isrepresentative of only one of many preferred embodiments for suchpumping stripes, as many other configurations are realizable to meet theobjectives of this invention, which includes reduced pumping at thenarrow end of diverging gain section 10B to permit initial spread of thelight beam fully into the boundaries of the gain section prior tointensive pumping to permit improved optical power enhancement of thebeam edges. These other configurations are shown in FIGS. 10A to 10E.The patterns shown are for purposes of exemplification in that thenumber or area size of the stripes or pattern can be varied in anynumber of ways, such as, by increase in the number of pattern stripes orpoints by reducing their size and increasing their density, or renderingthe pattern stripes or points all the same size or rendering them tohave a monotonically increasing area size from aperture 23 into section10B. Moreover, the patterns can be interspersed, such as, for example,the dot pattern shown in FIG. 10B may be placed at the narrow end ofsection 10B adjacent to aperture 23 followed by the stripe pattern withconverging end tails shown in FIG. 10D. In another aspect, the pumpingpattern is void at the outer reaches 27A of the diverging section, i.e.,along diverging edges 27A of section 10B, the pumping pattern is notpresent to interfere with the beam spreading and filling function.

In FIG. 10A, pumping pattern 50 consists of elongated pumping stripesextending fairly in the direction of the propagating light and in thedirection of the optical axis of device 10. Stripes 50 may of uniformwidth or of monotonically increasing width, as indicated by thedifferent stripe width at 51 compared to 52, to monotonically increasepumping intensity of the propagating light as it progresses further intothe narrow end of section 10B. Also, the most central stripes 53 may beof larger area or size to accommodate greater pumping of the higherpower portion of propagating Gaussian-shaped light beam while the beamspreads and fill to edges or boundaries 27A of the diverging gainsection. In FIG. 10B, a pattern of pumping dots 55 is formed which maybe all of the same size or of progressively increasing size fromaperture 23 forward into section 10B in the direction of arrow 56, asshown in FIG. 10B, from small size at 57 to a largest size at 58. In thecase of a dot pattern of dots of the same size (not shown), preferablythe density of the dots would be less at aperture 23 in the beginning ofdiverging section 10B and monotonically increase in their density in thedirection arrow 56. The point pattern of FIG. 10B may be of any otherkind of configuration, such as triangular shaped components 60 shown inFIG. 10C. Triangular shaped pattern regions or dots 60 may be all of thesame size with monotonically increasing density or of monotonicincreasing size in the direction of arrow 61 from a smallest size 62 toa largest size 63.

FIGS. 10D and 10E illustrate variations in the stripe pattern 27 of FIG.1. The pattern strips 65, 70 are dimensionally largest in their centralregion where the propagating Gaussian-shaped light beam is the strongestin terms of optical power. These patterns permit initial comparativelystronger pumping of the beam while permitting the beam to spread andfill the diverging section to edges 27A where there are no pumpingstripes present. The shape of the stripes 65, 70 may converge laterallyat their opposite ends toward edges 27A in a manner or at a rate ofsimilar to the Gaussian-shaped light beam pattern. In FIG. 10D, stripepattern 65 comprises a plurality of transversely disposed stripes withconverging ends terminating prior to reaching the diverging edges 27A.The pattern stripes 65 may be of the same width (not shown) withmonotonically increasing length with either the same spacing or periodor with monotonically decreasing interspacing to progressively increasetheir density. As shown in FIG. 10D, stripes 65 are of monotonicallyincreasing size in the direction of arrow 66 progressing from stripe 67to stripe 68 with substantially the same spacing. Pattern 70 in FIG. 10Eis similar to pattern 65 of FIG. 10D except that the stripes are of morediamond shaped pattern with the widest portion of the pattern stripescentral of the strongest portion of the optical power of the propagatingGaussian-shaped light beam. Stripes 70 may be of monotonicallyincreasing dimension in the direction of arrow 71 progressing fromstripe 71 to stripe 73.

FIG. 5 is shows pump stripe pattern 26, 27, 28 for device 10 drawnfairly to scale (with a portion of single mode strip 26 omitted due tolength). The relationship of the lengths of pump sections 33, 34 and 35are important for obtaining an optimized device operation. A longerpattern and cavity length improves the diffraction limited power of theresultant beam but threshold efficiency will be degraded so that someefficiency is compromised in order to achieve improved beam quality. Therelationship between the length of single mode stripe 26 and the lengthof diverging gain region 10B comprising contact regions 27 and 28 is oneof design from the standpoint of current density distribution. In atypical device, single mode section 10A may be about 40% of the cavitylength while beam diverging gain section 10B may be about 60% of thecavity length. The patterned stripe section 34 may be about 5% to about20% of the entire length of section 10B, e.g. about one-tenth of thesize of section 10B. The formed stripes 27 in section 34 may be of equalspacing period or may have a period greater than the width of individualpumping stripes 27, e.g., their period 32 may about 25 jim and thestripe width 31 may be about 5 μm wide. However, there is no need forfixed relationship of this pattern as long as input section 34 issubjected to reduced pumping activity to accomplish the purpose of thisinvention. The stripe pattern section tailors the current so that thelight beam 37A emerging from aperture 23 will have an initialopportunity to diverge laterally into the narrow end expanse ofdiverging gain section 10B prior to intense current pumping that takesplace in pumping region 28. By permitting the beam to initially expandbefore aggressive gain pumping, the beam is permitted to fill andestablish its divergence property insuring improved gain saturation ofthe propagating beam edges when it enters into pumping region 28. Theeffect of edge gain enhancement is illustrated in FIG. 5 by transversemode waveforms 37. The beam transverse mode profile 36 in single modesection is, of course, quite small. As the light beam emerges at 37Afrom aperture 23, the beam is not strongly pumped in section 34 toprovide an opportunity to expand, as explained above. In section 35, theentire lateral width of the beam is continually subjected to gainpumping as it continues to diverge toward the output. The beam havingalready filled and established the divergence pattern across thediverging gain section 10B, improved saturation can be achieved alongthe entire beam lateral phase front. As indicated by the progressivelyexpanding beam profiles 37B-37E, the beam becomes more of a flattenedand broadened Gaussian beam profile with resultant higher saturation ofpropagating light edge portions 38, as illustrated at profile 37E,rendering a more laterally uniform beam profile. With the use of acarbon or boron implant to form high resistance regions 30, only a smallrefractive index change occurs along diverging edges 27A providing weakindex guiding permitting the propagating light evanescent tails 38 to bemore uniformly enhanced as the light beam spreads into diverging gainsection 10B.

It should be noted that sections 34 and 35 may be pumped from a singlesource or may be differentially pumped with different current values orpumped at modulated pumping rates as taught in the incorporated patents,in particular, incorporated U.S. Pat. No. 5,539,571. Also, as taught bythe several incorporated patents, sections 10A and 10B may beindependently pumped to provide for fine tuning of the power of the beamoutput.

Reference is now made to FIGS. 6 and 8 which show a detailed plan viewof the pumping stripe regions of device 10. The purpose of FIGS. 6 and 8is to illustrate a particular preferred pattern for single mode stripe26. FIG. 8 is a more detailed view of a portion of stripe 26 forpurposes of later comparison with FIG. 9. Stripe 26 may have twoportions, a uniform width portion 26A, e.g., about 4 μm, and a taperedportion 26B which tapers or narrows in width to aperture 23, e.g. 2 μm.Uniform width portion 26A of single mode section 10A permits a portionof this section to be of wider extent to provide for more current flowand higher current density with corresponding higher carrier conversionefficiency utilizing the affect of transitional layers 12, 20 and 21, aspreviously discussed. Tapered portion 26B contributes to establishingthe desired beam divergence via aperture 23 into the diverging gainsection 10B where the size of aperture 23 is roughly proportional to theFWHM of the propagating light beam. The beam divergence rate isestablished by the size of aperture 23, i.e., the smaller the aperture23, the larger the beam divergence into diverging gain section 10B.Diverging beam section 10B beginning at aperture 23, laterally opensimmediately into an area starting at section end 27B that is wider thanaperture 23 to permit the propagating light to immediately expand,spread and fill into the region of patterned current pumping stripes 27along diverging edges 27A. The current pumping pattern of stripes 27 insection 34, as previously explained, provides an opportunity for thepropagating beam to expand at the desired angle of divergence prior tosaturated gain pumping to significantly increase the optical power ofthe output beam.

FIG. 7 is the same as FIG. 6 except that the current confinement regionformed with n-p-n blocking layer 22A is extended from line 29, shown inboth FIGS. 1 and 6, to a position within diverging gain section 10B atlines 29A forming wing-like lightwave absorber regions 44. Lightwaveabsorbing regions 44 in areas outside of semiconductor gain region 28absorb light reflected back into the optical cavity length from facet10D and diverted at an angle other than normal to the optical axis ofdevice 10. Therefore, only a small portion of reflected light from facet10D enters as feedback through aperture 23 into single mode section 10A.

FIG. 9 illustrates an alternative embodiment to the tapered stripesection 10A of FIG. 6. In FIG. 8, the tapered portion 26B may be a smallportion of the length of section 10A, e.g., about one-tenth of thelength of section 10A. This provides for a sufficiently wide stripe forpumping purposes before attendance to the divergence angle requirementsof the propagating beam established by aperture 23.

Alternatively, tapered portion 26B may extend along more of the lengthof single mode section 10A, if desired, and extended to end facet 10C asillustrated by tapered section 26C in FIG. 9.

The visible wavelength, optoelectronic device 10 provides aGaInP/AlGaInP/GaAs material system that can deliver a room temperature,high CW power, diffraction limited, single transverse mode beam. As anexample, device 10, illustrated in FIG. 1, may provide a 500 mW singlemode beam with a 1.5 mm FW 1/e² beam diameter and having a wavelength ofabout 680 nm, ±10 nm, with a 5 nm spectral bandwidth enabling efficientenergy coupling into solid state host mediums, print media or employedas a highly visible display beam. The threshold operating current isabout 0.75 A with an operating current of about 2.3 A and device seriesresistance of about 0.2 Ω. Device 10 may be mounted on a diamondsubmount with a TEC cooler.

Although the invention has been described in conjunction with one ormore preferred embodiments, it will be apparent to those skilled in theart that other alternatives, variations and modifications will beapparent in light of the foregoing description as being within thespirit and scope of the invention. Thus, the invention described hereinis intended to embrace all such alternatives, variations andmodifications as that are within the spirit and scope of the followingclaims.

What is claimed is:
 1. A multilayer semiconductor optoelectronic devicecomprising: a semiconductor gain region having diverging side edgesextending from a first end of the region to a second end of the regionfor allowing divergence of light propagating along its cavity lengthbetween said edges; regions outside of said semiconductor gain regionand at least along a portion thereof between said first and second endscomprising high resistance regions.
 2. The multilayer semiconductoroptoelectronic device of claim 1 wherein said high resistance regionsare incorporated with boron or carbon.
 3. The multilayer semiconductoroptoelectronic device of claim 2 wherein said incorporation is carriedout by implantation.
 4. The multilayer semiconductor optoelectronicdevice of claim 1 further comprising lightwave absorbing regions in aportion of said regions outside of said semiconductor gain region wallsto absorb light reflected back into its cavity length and penetratingthrough said walls.
 5. The multilayer semiconductor optoelectronicdevice of claim 1 wherein a single mode region is optically coupled viaan aperture to said semiconductor gain region.
 6. The multilayersemiconductor optoelectronic device of claim 5 further comprising atapered portion in at least a portion of said single mode regionextending to said aperture.
 7. The multilayer semiconductoroptoelectronic device of claim 6 further comprising a plurality ofspatially disposed pumping stripes formed in a portion of saidsemiconductor gain region in proximity to said aperture.
 8. An unstableoptical resonator comprising: single spatial filter section and abroadened gain section optically coupled to said single spatial filtersection; an optical resonator cavity formed with said sections forpropagating light; a loss-guide mechanism in said single spatial filtersection defining a pumping stripe; reduced band offset in said singlespatial filter section to improve carrier density upon pumping saidsection via said pumping stripe; said broadened gain section havingdiverging side edges extending from said single spatial filter sectionto an opposite end of said broadened gain region; high resistanceregions formed along at least a portion of said edges outside of saidbroadened gain section between said single spatial filter section andthe opposite end of said broadened gain section; refractive indexvariance between said high resistance regions and said diverging gainregion being small to provide for loss-guiding of said propagatinglight.
 9. The unstable optical resonator of claim 8 wherein said highresistance regions are formed by incorporation of boron or carbon. 10.The unstable optical resonator of claim 8 wherein said loss-guidemechanism is high index Group III-V material defining the boundaries ofa pumping stripe in said single spatial filter section.
 11. The unstableoptical resonator of claim 10 wherein said mechanism is a three-tierlayer of GaAs.
 12. The unstable optical resonator of claim 8 whereinsaid diverging gain region includes a partially gain pumped portion toinitially receive said propagating light from said single spatial filtersection.